A high-tension installation and an assembly of this type are known from U.S. Pat. No. 4,024,339. A first tube-like encasing part includes an end flange, designed as an outer flange, with through bores disposed on a part circle coaxial with the axis of the first encasing part. A second encasing part with a similarly designed end flange is disposed in alignment with the first encasing part, through bolts passing through from the second encasing part freely through the through bores in the end flanges, the through bolts being supported by nuts at the end flange of the first encasing part. Seen in the radial direction, a securing ring is disposed within the through bolts between the end flanges of the first and second encasing parts, which securing ring is secured by means of cap screws to the end flange of the first encasing part. The internal envelope surface of this securing ring is, seen from the first encasing part, designed to be conically tapering, in order to retain an insulator and to press the insulator onto a ring-like sealing element between the insulator and the end flange of the first encasing part. The insulator carries, centrally, a tube-like current conductor and the encasing spaces defined by the first and second encasing parts are partitioned off from one another.
With the second encasing part removed from the first encasing part, the securing ring holds the insulator in sealed connection firmly on the first encasing part, forming an assembly with the first encasing part which is ready for dispatch and is suitable for local mounting. In this case, the insulating gas in the encasing space of this assembly is usually only slightly above ambient pressure for transport and mounting. When mounting the high-tension installation has been completed, the insulating gas is placed under the pressure required for the pertinent voltage.
In the case of this known high-tension installation, the bolts connecting the first and second encasing part to one another are outwardly displaced with respect to the securing ring. This involves appropriately large dimensions of the end flanges, as well as a large number of bolts of high strength. Due to the required large diameters of the end flanges, the space required by the high-tension installation is also large.
Further, in the case of a high-tension installation as is known from Sprecher and Schuh (Catalog No. 47 B1) "Metal-encased, SF.sub.6 -insulated high-tension installations, type B 212" (1977), the securing rings are screwed by means of through bolts onto the corresponding end flanges. In this case, the part circle of these through bolts is the same as the part circle of those through bores in the end flanges and in the securing rings which are penetrated by the through bolts stressing the encasing parts relative to one another. The through bolts which hold the securing rings on the corresponding end flanges are only required until the two encasing parts are firmly screwed to one another. This is necessary for guaranteeing gas sealing of the assembly during transport as an assembly until the mounting of the high-tension installation and for holding the active parts carried by the insulator. For a high-tension installation of this type, the through bolts fastening the securing rings to the end flanges require considerable space in addition to the through bolts which are required to secure the encasing parts to one another. In this case also, the end flanges are required to be large.
Furthermore, DE-A-2,157,101, which corresponds to U.S. Pat. No. 3,809,795, discloses a high-tension installation in which the insulator is disposed on a securing ring. The latter includes blind bores with threads, on both sides, into which cap screws penetrating the end flanges of the corresponding encasing parts are inserted. Thus, the encasing parts are screwed exclusively to the securing ring. This structure also requires securing rings of considerable axial thickness.